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331
Adobe Photoshop Help
Applying Filters for Special Effects
Using Help
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Contents
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331
To use the Dust & Scratches filter:
1
Choose Filter > Noise > Dust & Scratches.
2
If necessary, adjust the preview zoom ratio until the area containing noise is visible.
3
Drag the Threshold slider left to 0 to turn off the value, so that all pixels in the selection
or image can be examined.
The Threshold determines how different the pixels’ values should be before they are
eliminated.
Note:
The Threshold slider gives greater control for values between 0 and 128—the most
common range for images—than for values between 128 and 255.
4
Drag the Radius slider left or right, or enter a value in the text box from 1 to 16 pixels.
The radius determines how far the filter searches for differences among pixels.
Adjusting the radius makes the image blurry. Stop at the smallest value that eliminates the
defects.
5
Increase the threshold gradually by entering a value or by dragging the slider to the
highest value possible that eliminates defects.
Median
Reduces noise in an image by blending the brightness of pixels within a
selection. The filter searches the radius of a pixel selection for pixels of similar brightness,
discarding pixels that differ too much from adjacent pixels, and replaces the center pixel
with the median brightness value of the searched pixels. This filter is useful for eliminating
or reducing the effect of motion on an image.
Pixelate filters
The filters in the Pixelate submenu sharply define a selection by clumping pixels of similar
color values in cells.
Color Halftone
Simulates the effect of using an enlarged halftone screen on each
channel of the image. For each channel, the filter divides the image into rectangles and
replaces each rectangle with a circle. The circle size is proportional to the brightness of the
rectangle.
To use the Color Halftone filter:
1
Choose Filter > Pixelate > Color Halftone.
2
Enter a value in pixels for the maximum radius of a halftone dot, from 4 to 127.
3
Enter a screen-angle value (the angle of the dot from the true horizontal) for one or
more channels:
•
For Grayscale images use only channel 1.
•
For RGB images, use channels 1, 2, and 3, which correspond to the red, green, and blue
channels.
•
For CMYK images, use all four channels, which correspond to the cyan, magenta, yellow,
and black channels.
•
Click Defaults to return all the screen angles to their default values.
4
Click OK.
